It is most desirable for printers, for example those employing energy curable (e.g., ultra violet or electron beam curable), to generate printed products with the highest resolution and quality. However, numerous problems ensue when attempting to provide high resolution in that the printing quality suffers. The major problem in printing at high resolution is ensuring that each drop of printed ink contains enough pigment to produce a bright vibrant color. Simply loading more pigment to the printing ink causes other defects that adversely affect its quality, such as the occurrence of unwanted high viscosity and poor printing quality. Incorporation of known dispersants help to neutralize some defects but they do not provide for low viscosity, high gloss and high print quality.
U.S. Pat. No. 6,110,264 discloses a phase change ink composition where one component is an anhydride/alcohol or amine inclusive product. Mixed reaction products include carboxylic acid/amide/imide/ester as carriers only and only for use in phase change ink jet systems. U.S. Pat. No. 6,037,414 describes a graft polymer composed of an acrylic polymer backbone and pending from it polyester side chains, cyclic imides, and quaternary ammonium groups. The polymers result in compatibility problems and therefore printing quality problems. U.S. Pat. No. 5,688,312 discloses a hot melt ink composition that contains molecules possessing imide or bisimide groups. The imides are obtained by the reaction of a polyoxyalkylene amine with various phthalic anhydride or succinic anhydride derivatives. The molecular structure of these dispersants does not contain any free carboxylic acid groups which is required to properly bond the dispersant to the laked pigments. U.S. Pat. No. 5,286,873 discloses an imide-linked polymer dispersant for lubricating oils obtained by reacting polyisobutylene anhydride with a polyoxyalkylene amine for use in eliminating piston varnish and sludge in an internal combustion engine. U.S. Pat. Nos. 4,754,056 and 4,673,705 both describe an ultra-violet curable polymeric dispersant possessing acrylate functional groups in the backbone. Also, the polymer possesses free carboxyl groups that assist in wetting the pigment and in stabilizing the dispersion. However, the dispersant is not compatible with solvent systems and also has printing quality problems. U.S. Pat. No. 4,496,686 discloses a dispersant obtained by reaction of a polycarboxylic acid anhydride having a molecular weight of 100-4000 with an alcohol or a primary amine, forming the corresponding half ester or half amide respectively. The dispersant is used in radiation-curable inks and coatings but has printing quality problems.
Thus, there exists a need for an appropriate dispersant for use in formulating printing inks which provides for more efficient wetting and deflocculation of the pigment, affording a more stable dispersion and thereby providing high print quality such as high gloss and low viscosity.